The invention relates generally to the purification of gaseous substances. Of particular interest to the invention are a method and arrangement for the purification of gaseous substances using adsorption, and especially a method and arrangement for removing oxides of sulfur from waste gases at temperatures between about 80.degree. and 160.degree. C using carbonaceous adsorbents.
It is known that waste gases such as, for example, the combustion gases of power plants, may be desulfurized at temperatures between about 80.degree. and 160.degree. C by the adsorption of sulfur dioxide on carbonaceous adsorbents. In the adsorber, the adsorbed sulfur dioxide (SO.sub.2) oxidizes to SO.sub.3 which, in turn, leads to the formation of sulfuric acid. These reactions, as well as the adsorption process, liberate heat so that a temperature increase occurs in the adsorbent. During the operation of the apparatus in which the adsorption takes place, the liberated heat is removed from the adsorber by the flowing waste gases so that no substantial temperature increase occurs in the adsorbent.
When the adsorber is put out of operation, uncontrolled quantities of air are sucked into the adsorber. This is due to the fact that the adsorption process is carried out at subatmospheric pressures. Thus, since unavoidable leaks are present in the apparatus, and since the power plant and the exhaust stack through which the purified waste gases are exhausted generate a suction effect, currents of air will be drawn into the adsorber. These currents of air constitute a fresh source of oxygen and, as a result, reaction of the adsorbed sulfur dioxide continues. In turn, heat continues to be liberated in the adsorber. However, since the flow of the waste gases has been discontinued, the liberated heat is no longer being removed from the adsorber so that a temperature increase can occur in the adsorbent. The temperature increase may be so large as to cause combustion of the carbonaceous material used as an adsorbent.